.TH std::ranges::pop_heap 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::pop_heap \- std::ranges::pop_heap

.SH Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::random_access_iterator I, std::sentinel_for<I> S,

             class Comp = ranges::less, class Proj = std::identity >
   requires std::sortable<I, Comp, Proj>                              \fB(1)\fP \fI(since C++20)\fP
   constexpr I

       pop_heap( I first, S last, Comp comp = {}, Proj proj = {} );
   template< ranges::random_access_range R, class Comp =
   ranges::less,

             class Proj = std::identity >                             \fB(2)\fP \fI(since C++20)\fP
   requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
   constexpr ranges::borrowed_iterator_t<R>

       pop_heap( R&& r, Comp comp = {}, Proj proj = {} );

   Swaps the value in the position first and the value in the position last - 1 and
   makes the subrange [first, last - 1) into a max heap. This has the effect of
   removing the first element from the heap defined by the range [first, last).

   1) Elements are compared using the given binary comparison function comp and
   projection object proj.
   2) Same as \fB(1)\fP, but uses r as the range, as if using ranges::begin(r) as first and
   ranges::end(r) as last.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   first, last - the range of elements defining the valid nonempty heap to modify
   r           - the range of elements defining the valid nonempty heap to modify
   pred        - predicate to apply to the projected elements
   proj        - projection to apply to the elements

.SH Return value

   An iterator equal to last.

.SH Complexity

   Given N = ranges::distance(first, last), at most \\(\\scriptsize 2\\log{(N)}\\)2log(N)
   comparisons and \\(\\scriptsize 4\\log{(N)}\\)4log(N) projections.

.SH Notes

   A max heap is a range of elements [f, l), arranged with respect to comparator comp
   and projection proj, that has the following properties:

     * With N = l - f, p = f[(i - 1) / 2], and q = f[i], for all 0 < i < N, the
       expression std::invoke(comp, std::invoke(proj, p), std::invoke(proj, q))
       evaluates to false.
     * A new element can be added using ranges::push_heap, in \\(\\scriptsize
       \\mathcal{O}(\\log N)\\)𝓞(log N) time.
     * The first element can be removed using ranges::pop_heap, in \\(\\scriptsize
       \\mathcal{O}(\\log N)\\)𝓞(log N) time.

.SH Example


// Run this code

 #include <algorithm>
 #include <array>
 #include <iostream>
 #include <iterator>
 #include <string_view>

 template<class I = int*>
 void print(std::string_view rem, I first = {}, I last = {},
            std::string_view term = "\\n")
 {
     for (std::cout << rem; first != last; ++first)
         std::cout << *first << ' ';
     std::cout << term;
 }

 int main()
 {
     std::array v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
     print("initially, v: ", v.cbegin(), v.cend());

     std::ranges::make_heap(v);
     print("make_heap, v: ", v.cbegin(), v.cend());

     print("convert heap into sorted array:");
     for (auto n {std::ssize(v)}; n >= 0; --n)
     {
         std::ranges::pop_heap(v.begin(), v.begin() + n);
         print("[ ", v.cbegin(), v.cbegin() + n, "]  ");
         print("[ ", v.cbegin() + n, v.cend(), "]\\n");
     }
 }

.SH Output:

 initially, v: 3 1 4 1 5 9 2 6 5 3
 make_heap, v: 9 6 4 5 5 3 2 1 1 3
 convert heap into sorted array:
 [ 6 5 4 3 5 3 2 1 1 9 ]  [ ]
 [ 5 5 4 3 1 3 2 1 6 ]  [ 9 ]
 [ 5 3 4 1 1 3 2 5 ]  [ 6 9 ]
 [ 4 3 3 1 1 2 5 ]  [ 5 6 9 ]
 [ 3 2 3 1 1 4 ]  [ 5 5 6 9 ]
 [ 3 2 1 1 3 ]  [ 4 5 5 6 9 ]
 [ 2 1 1 3 ]  [ 3 4 5 5 6 9 ]
 [ 1 1 2 ]  [ 3 3 4 5 5 6 9 ]
 [ 1 1 ]  [ 2 3 3 4 5 5 6 9 ]
 [ 1 ]  [ 1 2 3 3 4 5 5 6 9 ]
 [ ]  [ 1 1 2 3 3 4 5 5 6 9 ]

.SH See also

   ranges::push_heap     adds an element to a max heap
   (C++20)               (niebloid)
   ranges::is_heap       checks if the given range is a max heap
   (C++20)               (niebloid)
   ranges::is_heap_until finds the largest subrange that is a max heap
   (C++20)               (niebloid)
   ranges::make_heap     creates a max heap out of a range of elements
   (C++20)               (niebloid)
   ranges::sort_heap     turns a max heap into a range of elements sorted in ascending
   (C++20)               order
                         (niebloid)
   pop_heap              removes the largest element from a max heap
                         \fI(function template)\fP
